Amazon.com: UB645 Universal Sealed Lead Acid Battery Replacement (6V, 4.5Ah, 4500mAh, F1 Terminal, AGM, SLA) - Includes TWO F1 to F2 Terminal Adapters - Compatible with Kung Long WP4.5-6, Sheng Yang SY640,
BatteryGuy BG-640 6V 4AH Replacement for Sheng Yang SY640 (2 Pack, rechargeable) - Walmart.com